1. Field of the Invention
The invention relates to a method for bonding a wire which is coated with an insulating lacquer layer, on a contact element. The invention relates in particular to a bonding method for electronic components, such as HF-inductor coils having a wire wound around a ceramic, plastic or ferrite core.
2. Description of the Related Art
In electrical components, such as relays or contactors, a continuing trend toward miniaturization requires that the inductor coils employed be made as small as possible. This means that the wires used in winding, have a very small diameter, as a result of which, the bonding of the coil ends becomes more difficult. As an example, the end of the coil may exhibit diameters in the order of 30 to 100 .mu.m (0.03-0.1 mm). In German patent application No. P 34 33 692.3 (U.S. Ser. No. 761,288); a miniaturized HF-inductor of this type in chip form is disclosed. In this chip a lacquer insulated wire which may be wound in one or more layers, must be bonded to plate-like contact elements.
Until the present time, lacquer coil connections were bonded by manual, mechanized or fully automated soldering. Particularly in the case of high temperature lacquered wires, temperatures as high as 500.degree. C. are necessary. Thus, the materials immediately adjacent to the soldering area may be damaged by the radiated heat.
Ultrasonic welding, in which the lacquer insulation layer is broken up and welding action is accomplished simultaneously, may be applied to advantage for bonding. However, problems arise in lacquer insulated wires less than 0.4 mm, since the wire is weakened at the point of attachment due to deformation. Since the mechanical requirements imposed cannot be met in general, it has been necessary until now, to weld with an additional small covering plate in order to improve the mechanical attachment. The foregoing is described specifically for laser welding in laid open German patent application No. 33 07 773. In the fabrication of HF-inductor coils, which are produced either with terminal leads, or more recently with terminal lugs as so-called HF-inductor-chips, this would mean higher cost, since the small covering plates must be handled prior to welding.